I’ve tried changing the DRB port to 20111 and running rake pre_commit
again but the same problem comes up. Is this something people have
come across before?

I actually just noticed it a couple of days ago. I was able to resolve
it by building and installing the rspec gem, so there is an apparent
dependency on that being present. We’re going to be re-vamping (readsimplifying) the whole rspec-dev setup in the next month or so, so
I’m not going to try to fix this right now, but installing the gem
should solve it for you.